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Re: Refraction
From: Frank Reed CT
Date: 2005 Aug 27, 00:51 EDT
From: Frank Reed CT
Date: 2005 Aug 27, 00:51 EDT
Marcel, you wrote: "Does the Nautical Almanac have a different table than the previously mentioned table 6 from Pub. No. 249? If so, which title, page number etc.? Or, is there an other possibility to obtain it, instead of ordering it from "my" library abroad?" It's distinct from the table in pub. 249. The latter tables are intended for aviators so they include calculations for higher observer altitudes and they are rather low accuracy. The refraction tables in the Nautical Almanac are precise to the nearest tenth of a minute of arc and extend right down to the horizon in small steps. They are limited to observations made close to sea level. Do you want copies? You asked: "Wouldn't it be possible to find the authors of the table and ask them which model they used und why? Or, are there some clarifying comments in the Almanac?" There is no clarification in the almanac. The refraction tables published there were fixed and unchanging for fifty years. They were modified very slighly just a couple of years ago. Myself, I'm not too worried about how they calculated either the original table or the new version since we can calculate almost exact matches using simple atmospheric models. And that's good enough, as far as I'm concerned. Additionally, the difference between the new table and the old table is considerably smaller than the expected daily variations from layering in the lower atmosphere. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars